Inversion of 17 beta-steroids has been accomplished using a modified M
itsunobu protocol in which 4-nitrobenzoic acid is employed as the acid
ic component. Excellent yields of inverted product were obtained for a
number of representative steroid families including estrogens, equile
nins, and androgens. Application of this methodology to the synthesis
of 17 alpha-dihydroequilenin is described.